This invention relates to the programming of a central receiving unit in a remote tire monitoring system to identify sending units such as radio frequency tire pressure sending units associated with the vehicle.
U.S. Pat. No. 5,600,301, assigned to the assignee of the present invention, discloses a tire pressure monitoring system that includes sending units associated with each tire of a vehicle and a central receiving unit. Each of the sending units includes a respective radio frequency (RF) transmitter that transmits an RF signal. The RF signal includes both an identifier code and an indicator of tire pressure. Additionally, each of the sending units includes a magnet sensor. When the receiving unit is placed in a learn mode, a magnet is used to activate each sending unit of the vehicle in a predetermined order. The receiver learns the identifiers associated with the respective tires based upon the sequence of activation of the sending units. This approach is found reliable in use, while it requires the use of a suitable magnet for activating the sending units.
In one patent application assigned to the assignee of the present application, a remote tire pressure monitoring system includes a sending unit for each monitored tire. The sending units transmit RF signals including an identifier and a pressure indicator. A receiver operates in a learn mode in which the receiver associates specific identifiers either with the vehicle or with specific tires. During the learn mode, the vehicle is driven at a speed above a threshold speed and identifiers are associated with either the vehicle or the respective tires of the vehicle only if they persist for a selected number of signals or frames during the learning period. In one example, the tires are inflated with different pressures according to a predetermined pattern and the pressure indicators of the receive signals are used to associate individual tire positions with the respective sending units.
Other techniques for identifying the position of a transmitting tire monitor are known. In U.S. Pat. Nos. 5,483,827 and 5,661,651, the frequency of transmission is used to identify and distinguish the tire monitor which originated the transmission.
Other techniques for a programming a receiving unit with tire position information involve manual entry of the information. This has been done by using a keypad to enter both the tire monitor identification information and tire position information. This has also been done by using a bar code to read the tire monitor identification information directly from the tire monitor while still manually entering the tire position information.
The approaches discussed above are not fully automatic. An automatic technique is desired to improve reliability and convenience for the user.
By way of introduction only, the method and apparatus of the following description identify the position of tire monitors attached to a vehicle using a secondary modulation of the radio signals transmitted by each monitor. Each monitor imposes a primary modulation on signals it transmits using tire data related to tire pressure. In addition, other vehicle components such as metallic masses near the wheels impose secondary modulation on the radio signals transmitted by the tire monitor. This secondary modulation may be learned and decoded to identify the position associated with a signal received at the receiver. In addition, additional components may be attached near the wheel to modify and control the secondary modulation for subsequent retrieval by the receiver.
The foregoing discussion of the preferred embodiments has been provided only by way of introduction. Nothing in this section should be taken as a limitation on the following claims, which define the scope of the invention.